Wave-signal receiving system



Fab, 4, 194?. H. A. WHEELER WAVE-SIGNAL RECEIVING SYSTEM Filed MarCh 8, 1944 nA ,by .L a RH n Ow N V ,T R w NA O d E M. VD n NIL/M D. l0 D R A H Y B Patented Feb. 4, 1947;

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WAVE- SGNAL RECEIVING SYSTEM Harold A. Wheeler, Great Neck, N. Y., assigner, by mesne assignments, to Hazeltine Research, inc., Chicago, Ill., a corporation of Illinois Application March 8, 1944, Serial No. 525,523

9 Claims. l

This invention relates to wave-signal receiving systems and more generally to systems including superregenerative receivers which are relatively free from instability due to undesirable reflections of wave signals which are developed within the system.

In a, radio receiving system comprising an antenna and a transmission line for coupling the antenna to the receiver, it is desirable to match the impedance of the antenna and also the impedance of the input circuit of the receiver to the respective characteristic terminal impedances of the transmission line to minimize reections and to secure a maximum transfer of received signal energy from the antenna to the receiver. It' the impedance of the transmission line is mismatched to the antenna, or to both the antenna and the receiver input circuit, undesirable reflections arise when a signal is being translated by the system. These reflections are serious in superregenerative-type receivers which inherently radiate strongly during operation. Even when a signal is not being intercepted by the antenna, such a system may radiate a periodic signal, since the receiver alternately iiuctuates between an oscillatory and nonoscillatory state, as determined by the period oi the quench voltage and the amplitude of the generated oscillations depends upon the effective noise-signal input to the receiver. The periodic signal so produced in the oscillatory circuit of the receiverwhen applied to the transmission line, may develop troublesome reiiected signals when mismatch conditions cccur at the antenna and the receiver input terminals. These reections, when impressed on the receiver, prevent the oscillations which occur during a quench cycle from dying out within the proper time limit, specifically, in theA case where there is no desired signal input to the receiver, the generated oscillations are not attenuated below the thermal-agitation noise level before the build-up period of the next cycle of oscillations. As a result, oscillations are never entirely quenched in the manner required for proper operation and the receiver may oscillate continuously. rlhe same type of undesirable oscillations may occur when a desired signal is being received.

Prior art wave-signal receiving systems of the foregoing type, which include in the circuits thereof one or more impedance mismatches, have provided unsatisfactory operation under some conditions. Until the disturbing impedances are effectively matched, some of these prior art systems cannot be utilized for their desired purpose because of lack of stability. The matching of such impedances is somewhat complicated since it generally requires the connection and adjustment of one or more impedance-matching devices. It is desirable, therefore, to provide a receiver circuit of the general type under consideration in which some impedance mismatch oi the type mentioned above can be tolerated.

It is an object of the invention, therefore, to provide a wave-signal receiving system of the type under consideration which is free from one or more of the above-mentioned disadvantages of the systems of the prior art.

It is another object of the invention to provide, in a wave-signal receiving system of the character under consideration, relatively simple means for substantially attenuating undesirable reflections which are developed therein while effectively translating desired wave signals.

It is a furtherV object of the invention to provide in a wave-signal receiving system of the type under consideration, in which an impedance mismatch exists at the junction of the antenna system and the transmission line or at the foregoing junction and also at the junctionoi the transmission line and the input circuit of the receiver, means for substantially attenuating undesirable reflections resulting from the mismatch condition, thereby to provide stability in the system for received wave signals.

In accordance with the invention, a wavesignal receiving system the operation of which is relatively free from undesirable instability due to the influence therein of reflections of wave signals comprises an input circuit, a superregenerative receiving means having a quench period, and coupling means between the input circuit and the receiving means which has an eiiective electrical length such that the time interval required for the transmission of wave signals between the above-mentioned input circuit and the receiving means is at least an appreciable fraction of the quench period. The foregoing input circuit has an impedance which is mismatched to the. impedance of the coupling means to which it is coupled, so that undesirable reflections tend to be developed in the coupling means and applied to the receiving means. The system also includes means in circuit with the coupling means for substantially attenuating the undesirable reiiections to increase the stability of operation of said receiving means for received wave signals.

For a better understanding of the present invention, together with other and further objects thereof, reference kis had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a schematic circuit diagram of a superregenerativetype receiving system; while Figs. 2 and 3 comprise curves utilized in explaining the operation of the system of Fig. 1.

Referring now to Fig. 1 of the drawing, the system there illustrated includes an input circuit comprising an antenna system Il having a vertical radiator II and a horizontal conductive element I2, the latter forming a suitable ground plane. Radiator II may be a quarter-wave antenna, while element I2 may comprise the metallic surface of an aircraft. The system also comprises a superregenerative-type receiver having a regenerative oscillatory circuit I3 including an electron tube lli. The frequency-determining circuit of unit I3 comprises the parallel combination of an adjustable inductor I6, a tuning condenser lIl, and a condenser IS, which is shown in dotted lines for the reason that it may be comprised in whole or in part of the inherent capacitance of the circuit with which it is associated. The frequency-determining circuit is connected between the anode and the control electrode of tube I5 by condensers 2li and 2|. A source of potential, indicated -Ij-B, is connected to the anode of tube I4 through a choke winding 24. A choke winding and a cathode resistor 2 are connected in series between the cathode of tube I@ and ground. An adjustable bias for the control electrode of tube Ifl is provided by a suitable means, such as a source 3G which is grounded at its positive terminal and connected in circuit with a voltage divider 3l the adjustable tap of the voltage divider being connected to the control electrode of tube lil through a resistor 32 and a choke winding Sil. Quench-frequency signals are applied to the control electrode of tube I4 through a coupling condenser 35 and the winding 34 from a quench oscillator 36 of conventional construction. The mid-point of adjustable inductor i6 in the frequency-determining circuit is grounded.

The system also includes coupling means between the input circuit or antenna circuit I@ and the receiving means. This coupling means has an effective electrical length such that the time interval required for the transmission of wave signals between the antenna circuit and the receiving means is at least an appreciable fraction of the quench period of the receiving means. This coupling means comprises a transmission line 38, preferably of the coaxial type, connected between the antenna system I and a point on the inductor I5 of the regenerative oscillatory circuit of the receiver. The inner conductor 39 of the transmission line 38 is connected to the radiator I I and the outer conductor Il!! is grounded and connected to the conductive element I2.

Because of the diinculty in providing an exact impedance match, the antenna system Ill'generally has an impedance which is mismatched to the impedance of the transmission line 38 so that undesirable reections may be developed in the transmission line and applied to the receiving means and, specifically, to the inductor I5 in the regenerative oscillatory circuit I3. The wave-signal receiving system also includes means in circuit with the coupling means for substantialll7 attenuating the undesirable reilections to increase the stability of operation or the receiving means for received wave signals. This means comprises an L-type resistance attenuator 4I including a resistor i2 in series with inner conductor 39 of the transmission line and the tapping point on inductor it in the receiver, and a shunt resistor e3 connected at one end to the common junction of resistor G2 and the tapping point and at its other end to ground.

In order to detect the modulation-signal components of the signal developed in the regenerative oscillatory circuit i3, a diode detector l5 is provided. The anode of diode 5 is connected through a coupling condenser 13S to the common junction between condenser' 2| and inductor I6, while the cathode is connected to ground. A choke winding "9 and a load resistor 5U, which are connected in series between the anode oi' the diode t5 and ground, complete the direct current path for the detector. The input circuit of a modulation-signal amplifier 5i is connected across the load resistor 5S and the output circuit of the amplifier is connected to a signal-reproducing device 52.

Considering now the operation of the receiving system and assuming for the moment that the impedance of the antenna system il? is matched to the impedance of the transmission line 33 so that the inuence of attenuator 4l may be neglected, a wave signal is intercepted by the antenna system lil and translated by the transmission line 38 to the regenerative oscillatory circuit I3 of the receiver. Prior to the application of a received signal to the regenerative circuit I3, thermal-agitation noises and shot eiect periodically produce the initiating voltages which cause oscillations to be built up, only to be quenched or sup-pressed at recurrent intervals by voltages oi quench frequency which are supplied by the quench oscillator 3S to the control electrode of tube I il. When a received signal intercepted by the antenna system i is applied to the oscillatory circuit i3, the oscillations reach a much higher level and are sustained for a longer period before being quenched, thus imparting to the received signal a very high am.. pliflcation. rhe signal output of tube I4 is applied to diode 155 where the modulation components are derived across load resistor 5) for application to amplier 5I and, in turn, the signalreproducing device 52.

Referring no-w to Fig. 2 for the purpose of con- Sider-ing in more detail the operation of the system when no desired signal is being received, Curve A represents the signal which is developed curve represents the signal which is developed in the regenerative oscillatory circuit during this condition; curve B illustrates diagrammatically the quench voltage for application to the control electrode of tube i4', a rectangular wave form being selected to simplify the explanation; while curve C illustrates the variation of the receiver sensitivity with time. At approximately time to the receiver has its maximum sensitivity, and noise signals originating within the receiver circuit elements cause oscillations in circuit I3 to build up to a maximum value at time t1, as shown by curve A. During the negative-conductance period tu-t1 the quench voltage exceeds the critical level required for developing oscillations, while the sensitivity declines, as illustrated in curve C, to a minimum value at time t1. During the interval ril-ts, the quench voltage is less than the critical level .fc-:11, whereby oscillations in circuit i3 are suppressed. At time t1, the amplitude of the developed signal diminishes in the manner shown by curve A so that .at time t2 the oscillations are substantially completely attenuated; In the positive-conductance interval ti-ta,

the sensitivity of the regenerative circuit is pro-y iiculties arising from reflections when the im-k pedances of the antenna system and receiver are matched to that of the transmission line.

When the impedance of the antennaJ system is mismatched with respect to that of the transmission line, however, signals developed by unit I3 during a portion of the quench cycle are translated by the transmission line 38 to the antenna system i8 where a reflection occurs due to the mismatch and the reflected signals are translated by the transmission line and applied to unit i3 at a later time. At time t1, therefore, oscillatory signals of maximum amplitude are applied to line 38, are reflected by antenna system lll, and are impressed on the regenerative oscillatory circuit I3 at a later time. If the electrical length of the line 38 is such that the reflected oscillations are impressed on circuit I3 just before or approximately within the time interval 15e-t3, which interval is in the region ofl maximum sensitivity, oscillations in the regenerator will tend to build up to a high level, thereby providing sustained oscillations. This condition is not generally found in practice since the electrical length of the transmission line is usually shorter than for the condition assumed above. As a result, the action of quench oscillator 36, under the conditions assumed, no longer produces its desired eect and, consequently, the receiver does not fluctuate between an oscillatory and nonoscillatory condition in the superregenerative manner. Thus, where twice the time length of the transmission line 38, that is, twice the length measured in microseconds for a signal to be translated over the line, is approximately equal to one-quarter of the quench period, or the period of oscillator 36, undesirable reflections may seriously impair operation.

Consider now the operation of the system of Fig. l and taking into account the influence of attenuator 4| under the mismatch condition assumed above, the attenuation of the reflected signals in unit 4l is preferably suflicient to permit oscillations in the tuned circuit to be suppressed completely in the interval iti-tz. Hence, oscillations in the regenerative circuit are suppressed below the noise-signal level before the next negative-conductance period of the regenerator begins, so thatY the superregenerative receiver functions in a satisfactory manner even though a mismatch exists which, in the absence of the attenuator, would cause it to be inoperative. While desired received signals which are intercepted by the antenna system I and translated through the receiver are also attenuated by the unit 4l, this loss is more than offset by the benecial effect of the attenuator 4I on undesired reections which impair stability.

In Fig. 3 there is illustrated graphically the effect of multiple reflections on the tuned circuit of unit I3 when the input circuit lil and the receiving meansv each have impedances which are mismatched with respect to the terminal impedances of the transmission line 38. For the condition illustrated, the time delay of thetransmission line is short with reference to the quench period but is an appreciable fraction thereof and it israssumed that a desired received signa1 is not being intercepted by the antenna system lil. Transmission lines having a time delay, for example, of the order of jAgoth or more of the quench period, are frequently utilized. By

quench period is meant a quench cycle having a negative-conductance'portion and a positiveconductance portion, and the latter portion may,

in many cases, be of greater duration than the first-mentioned portion. Under these conditions, reiiections occur at each point of mismatch, namely, at the junction of the antenna and transmission line and also at the junction of the transmission line and the unit I3. Curve D of Fig. 3 represents the periodic signals which are developed by the regenerative oscillatory circuit and applied to the transmission line 33. Shortly after the crest portions of such signals are reected at the junction with the antenna system lil, the undesired reiiected signals are impressed on the tuned circuit of the receiver. Such undesired signals disturb tlie manner in which the stored energyvin the tuned circuit is dissipated during the period in which the original signals are being quenched. Instead of the` peak oscillation dying out along the gradual slope E during the interval tea-t7, the original signal thus decays in a series of echoes. The reflection of the peak oscillation and the multipley reflections resulting therefrom, which are applied to the oscillatory circuit i3, alter the performance of lthe tuned circuit and appear as a series of echoes G in the new envelope of the decaying oscillation during the quenching time. These echoes tend to prevent the oscillations from being completely quenched during the interval n-t. Therefore, the oscillations may not decay below the noise level before the next regenerative negativeconductance period which begins at time t8. As

a result, these undesired voscillations may hang over in the region of maximum sensitivity of' the receiver and, under such conditions, continuous oscillations build up in successive quench periods and the receiver becomes overloaded.

45 Considering now the operation of the system taking into account the effect of unit vll, the impedance mismatch at the junctions, referred to above, produces multiple reflections Which are substantially attenuated in unit di. Each trans- 50 lation of a reflected signal in either direction through attenuator M results in a material attenuation. The action of this unit, therefore, quickly attenuates the reflections so that the envelope of the positive-conductance portion of 55 curve D of Fig. 3 resembles the wave form J which is shown in dotted lines. It will be observed that the oscillations die out almost completely before the time t7 and, hence, are below the thermal-agitation noise-signal level before 60 the next negative-conductance period 'tat9 commences. This enables the receiver to operate in a normal manner to receive and reproduce den sired signals intercepted by antenna lll.

Under the conditions where the receiver oper- 65 ates satisfactorily with an attenuation in unit lll of, for example, three decibels for a desired received signal,` the unit il provides an attenuation which is effectively a multiple of that amount on the reflected signals during their 70 plurality of translations up and down the transmission line 38. Consequently, the receiver can be operated at a high gain, which gain may be many times three decibels, without instability of the type under consideration.

While there has been described what is at present considered lto be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changesy and modications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A Wave-signal receiving system the operation of which is relatively free from undesirable instability due to the iniiuence therein of reiiections of wave signals comprising, an input circuit, a superregenerative receiving means having a quench period, coupling means between said input circuit and said receiving means and having an effective electrical length such that the time interval required for the transmission of wave signals between said input circuit and said receiving means is at least an appreciable fraction of said quench period, said input circuit having an impedance whichis mismatched to the impedance of said coupling means to which it is coupled so that undesirable reilections tend to be developed in said coupling means and applied to said receiving means, and means in circuit with said coupling means for substantially7 attenuating said undesirable reiiections to increase the stability of operation of said receiving means for received wave signals.

2. A wave-signal receiving system the operation of which is relatively free from instability due to the innuence therein of reilections of Wave signals comprising, an input circuit, a superregenerative receiving means having a quench period, coupling means between said input circuit and said receiving means and having an effective electrical iength such that the time interval required icr the transmission of Wave signals between said input circuit and said receiving means is at least an appreciable fraction of said quench period, said input circuit having an impedance which is mismatched to the impedance of said coupling means to which it is coupled s o that undesirable renections tend to be developed in said coupling means and applied to said receiving means, and resistance means in circuit with said coupling means for substantially attenuating said 'undesirable reiiections to increase the stability of operation of said receiving means for received wave signals.

3. A wave-signal receiving system the operation of which is relatively free from undesirable instability due to the inuence therein of reilections of wave signals comprising, an input circuit, a superregenerative receiving means having a quench period and including a regenerative oscillatory circuit, coupling means between said input circuit and said receiving means and having an effective electrical length such that the time interval required for the transmission of wave signals between said input circuit and said regenerative oscillatory circuit is at least an appreciable fraction of said quench period, said input circuit having an impedance which is mismatched to the impedance of said coupling means to which it is coupled so that undesirable reflections tend to be developed in said coupling means and app-lied to said regenerative oscillatory circuit of said receiving means, and means in circuit with said coupling means for substantially attenuating said undesirable reflections to prevent continuous oscillations in said regenerative oscillatory circuit and to increase the stability of operation of said receiving means for received wave signals.

, 4. A wave-signal receiving system the opera--d tion of which is relatively free from undesirable instability due to the influence therein of reflections of Wave signals comprising, an input circuit for received wave signals, a superregenerative receiving means having a quench period, coupling means between said input circuit and said receiving means and having an effective electrical length such that the time interval required for thev transmission of wave signals between said input circuit and said receiving means is at least an appreciable fraction of said quench period, said input circuit having an impedance which is mismatched to the impedance of said coupling means to which it is coupled so that undesirable reiections tend to be developed in said coupling means and applied to said receiving means, and means in circuit with said coupling means for attenuating by a predetermined small amount said received wave signals and substantially attenuating said undesirable reflections to increase the stability of operation of said receiving means ior received wave signals.

5. A wave-signal receiving system the operation of which is relatively free from instability due to the inuence therein of renections of wave signals comprising, an input circuit, a superiegenerative receiving means having a quench period, coupling means between said input circuit and said receiving means and having an eiective electrical length such that the time interval required ior the transmission of wave signals between said input circuit and said receiving means is at least an appreciable fraction of said quench period, said input circuit and said receiving means having iinpedances which are mismatched with respect to the impedances or said coupling means to which they are coupled so that undesirable reections tend to b-e developed in said coupling means and applied to said receiving means, and means in circuit with said coupling means for substantially attenuating said undesirable reflections to increase the stability of operation oi` said receiving means for received wave signals.

6. A wave-signal receiving system the operation of which is relatively free from instability due to the influence therein of reflections of wave signals comprising, an input circuit, a superregenerative receiving means having a quench period, coupling means between said input circuit and said receiving means and having an effective electrical length such that the time interval required for the transmission of wave signals between said input .circuit and said receiving means is substantially less than said quench period but is at least an appreciable fraction of said quench period, said input circuit and said receiving means having impedances which are mismatched with respect to the impedances oi said coupling means to which they are coupled so that undesirable multiple reilections tend to be developed in said coupling means during each quench period and applied to said receiving means, and means in circuit with said coupling means for substantially attenuating said undesirable multiple reections to increase the stability of operation of said receiving means for received wave signals.

7. A wave-signal receiving system the operation of which is relatively free from instability due to the influence therein of reiiections of Wave signals comprising, an input circuit for received Wave signals, a sup'erregenerative receiving means having a quench period, coupling means between said input circuit and saidreceiving means and having an effective electrical length such that the time interval required for the transmission of wave signals between said input circuit and said receiving means is at least an appreciable fraction of said quench period, said input circuit `and said receiving means having impedanees which are mismatched with respect to the impedances of said coupling means to which they are coupled so that undesirable reflections tend to be developed in said coupling means and applied to said receiving means, and means in circuit with said coupling means for attenuating by a predetermined amount said received wave signals and attenuating said undesirable reflections effectively a multiple of said predetermined amount to increase the stability of operation of said receiving means for received wave signals.

8. A wave-signal receiving system the operation of which is relatively free from undesirable instability due to the influence therein of reflections of wave signals comprising, an antenna, a superregenerative receiving means having a quench period, a transmission line between said antenna and said receiving means and having an eiective electrical length such that the time interval required for the transmission of wave signals between said antenna and said receiving means is at least an appreciable fraction of said quench period, said antenna and said receiving means having impedances Which are mismatched with respect to the impedances of said transmission line to which they are coupled so that undesirable reflections tend to be developed in said transmissionv line and applied to said receiving means, and means in circuit with said transmission line for substantially attenuating said undesirable reflections to increase the stability of operation 0f said receiving means for received Wave signals.

9. A Wave-signal receiving system the operation of which is relatively free from undesirable instability from the influence therein of reflections of wave signals comprising, an antenna, a superregenerative receiving means having a quench period, a transmission line between said antenna and said receiving means and having an effective electrical length such that the time interval required for lthe transmission of Wave signals between said antenna and said receiving means is at least an appreciable fraction of said quench period, said antenna and said receiving means having impedances which are mismatched with respect to the impedances of said transmission line to which they are coupled so that undesirable reections tend to be developed in said transmission line and applied to said receiving means, and series resistor means and shunt resistor means in circuit with said transmission line for substantially attenuating said undesirable reflections to increase the stability of operation of said receiving means for receivedwave signals.

HAROLD A. WHEELER.

REFERENCES CTED The following references are of record in the le of this patent:

'UNITED STATES PATENTS Bly Dec. 31, 1940 

